The present invention relates to methods and apparatus for measuring distances between eyes and lenses. More particularly, the invention relates to such methods/apparatus for measuring the distance between an eye and a lens, for example, held in a phoropter or similar testing device such as a spectacle or trial frame, to facilitate the accurate prescription of a corrective lens for the eye being tested.
Many individuals require corrective lenses, e.g., eye glasses, contact lenses and the like. In order to determine the extent of the correction required, the individual's vision is tested using a phoropter or other optical measuring or testing device. In general, the testing device is placed in contact with the individual's face, for example, straddling the bridge of the nose, and the optometrist causes the individual to look through a series of lenses. This continues until the test lens providing the best vision quality is selected. The lens which is prescribed by the optometrist takes into account the optical power of the selected lens. Currently many clinicians use an average distance between the eye of the individual and the test lens (held in the testing device) is factored into the final lens prescription.
However, the actual distance between the test lens and the eye being tested varies substantially from individual to individual. This is so, for example, because of differences in facial bone structure from individual to individual. Thus, the average lens/eye distance which is customarily used in prescribing corrective lenses is only an approximation and very often introduces a diopter power error into the lens prescription.
Certain phoropters are provided with a mirror including graduations to give the clinician a measurement between the lens a nd eye. However, such graduated mirror has a limited range and is of limited usefulness, particularly in view of the restricted visibility that typically exists between the phoropter and the eye.
It would be advantageous to provide a system, for example, method and/or apparatus, for effectively measuring the distance between an individuals eye and the test lens selected as giving the best vision.